Following these steps you will achieve the same result without the need for an add-on:
1. Open Firefox. Type about:support.
2. Find where is says "Profile Folder " and click "Open Folder".
3. If it does not exist create a folder called Chrome.
4. In it create a text file called userChrome.css
5. Copy all of this into it:
.bookmark-item > .toolbarbutton-text {
margin-top: -1px !important;
}
#personal-bookmarks .bookmark-item:not(:hover):not([open="true"]) >
.toolbarbutton-text {
display: none !important;
}
#PlacesToolbarItems > .bookmark-item:not(:hover):not([open="true"]) >
.toolbarbutton-icon[label]:not([label=""]) {
margin-inline-end: 0px !important;
}
6. Save the file.
7. Restart Firefox.
That worked for me